1. Field of the Invention
This invention relates generally to tracheostoma valves.
2. Prior Art
In a human, a tube called the pharynx extends from the mouth down to the collarbone. A tube called the esophagus is connected between the pharynx and the stomach. A cartilaginous structure called the trachea is connected to the junction between the pharynx and the esophagus. A tube called the trachea is connected between the larynx and the lungs. Speech is produced by passing expiratory air from the trachea through the larynx and vibrating the vocal cords. The expiratory air is passed through the pharynx and out the mouth.
Sometimes the removal of the larynx, including the vocal cords, is necessitated by disease or injury. The trachea is diverted to exit the body at the base of the neck through a stoma (opening) to enable breathing. A tracheostoma valve is sometimes installed at the stoma for enabling bi-directional airflow during normal breathing. The valve is automatically closed under higher exhale pressures to redirect air from the trachea into the pharynx through a speech prosthesis extending there between. Speech is created by vibrating the air with muscles in the pharynx. The valve is sometimes installed at the end of a plastic tube inserted into the outer end of the trachea, and sometimes installed in a ring glued around the stoma.
U.S. Pat. Nos. 5,059,208 to Coe et al.; 4,582,058 to Depel et al.; and 4,325,366 to Tabor show tracheostoma valves. They are each comprised of a tubular housing with a flexible flapper membrane positioned close to a valve seat. The flapper membrane is normally spaced from the seat to allow bi-directional air flow during relaxed respiration. The flapper membrane is closed against the seat under higher exhale pressures to redirect air into the pharynx for speech production. However, the flapper membrane tends to flex too far away from the seat under high enough inhale pressure, such as that encountered during coughing, so that it would snap back onto the seat and make an embarrassing popping sound. The flapper membrane can only properly flex a small amount, so that it must be very close to the seat. The small gap between the flapper membrane and the seat tends to become clogged with body secretions, which makes the valve inoperative. Secretions also tend to foul the surface of the flapper membrane and prevent it from flexing properly.